1. Field of the Invention
The invention relates generally to an anticalculus dentifrice composition and more particularly to anticalculus dentifrice composition which is color stable on storage.
2. The Prior Art
Dental research has developed substantial evidence that beyond the age of 40 years loss of teeth is predominantly the result of periodontal involvement rather than dental caries. An important factor contributing to periodontal disease is the accumulation of dental calculus (e.g., salivary tartar) on the teeth. These deposits contribute to tissue inflammation of the surrounding gingiva, and, as the condition increases in severity, the supporting bone is also affected. These reactions lead to the destruction of the supporting structure and subsequent loss of teeth.
A wide variety of chemical and biological agents have been described in the art for retarding calculus formation or for removing calculus after it is formed. Included in the wide variety of chemical agents disclosed by the prior art as being effective as anticalculus agents are water soluble polyphosphate and pyrophosphate salts. For example, U.S. Pat. No. 4,627,977 discloses dentifrice composition containing one or a mixture of polyphosphate anticalculus salts such as water soluble alkali metal pyrophosphates, tripolyphosphates and hexametaphosphates, and a fluoride ion source, wherein salivary hydrolysis of P--O--P bonds in the polyphosphate salt is inhibited by the presence of 0.05 to 3 weight % of a polycarboxylate compound. When high concentrations of these polyphosphate salts are present in the dentifrice, e.g., 5-8% by weight, the pH of the dentifrice is in the alkaline range, i.e., in the range of about 8-10. U.S. Pat. No. 4,923,684 and U.S. Pat. No. 4,985,236 disclose the use of a water soluble alkali metal tripolyphosphate as an anticalculus agent contained in dentifrice compositions. The patent discloses that to be storage stable, the tripolyphosphate salt is incorporated in the dentifrice at a concentration of at least 4% by weight, the dentifrice having an alkaline pH, for example, a pH of 8-10.
In the preparation of the dentifrice compositions of containing high concentrations of polyphosphate anticalculus salts having an alkaline pH, it is desirable that sorbitol, in high concentrations, for example 30% by weight or more be used as a humectant as sorbitol is a relatively low cost material and imparts a desirable sweet flavor to the dentifrice. However, in dentifrice compositions in which the pH is above about 8, a browning discoloration of the dentifrice product is observed when commercially available sorbitol which normally contains 0.3% by weight reducing sugars such as mannitol is used in the dentifrice formulation. In addition to the undesirable discoloration of the product, an unpleasant flavor is imparted rendering the product undesirable for consumer use.